The synthetic generation of digital audio signals is used within the framework of sound synthesis for electronic generation of sounds. For this purpose, digital audio signals are used directly for sound synthesis immediately after their generation or, alternatively, stored in a storage unit for subsequent use. For the sound generation properly speaking, the digital audio signal is then used for activating a loudspeaker unit or the like, for example by means of a digital-analog transducer.
Sound synthesis is usually utilized for the purpose of generation of sounds which do not exist in nature. Another application is the imitation of natural sounds or natural instruments, such as piano, guitar or the like. Furthermore, sound synthesis also enables the specific or random coloration of natural sounds, for example by means of their superposition and processing with electronic effects, for a creative composition of music. Within the framework of synthetic generation of digital audio signals, one usually performs the periodic sampling of a suitably selected or predefined waveform or of an algorithmically generated signal, which gives as a result a value flow per channel (“resulting waveform”) with a fixed output rate (so-called sample rate) and a fixed value resolution (so-called bit depth), one value per channel per output-rate clock step being provided.
With regard to these parameters, the following fundamental influences upon the character of the digital audio signal are found:                The form of the resulting waveform determines the tone color.        The frequency of the repetitions of the resulting waveform determines the tone pitch.        If the resulting waveform changes from one repetition to the other, the tone color will change.        If the frequency of the repetitions changes, the tone pitch will change.        
To provide the waveform intended to be used as a basis for the sampling, usually a so-called oscillator is used, which can be modified as required, in accordance with the desired adaptation regarding tone pitch, tone color or other musical effects. Typically, oscillators generate waveforms with many partial tones, so that downstream processors as well as, typically, a low-pass filter, can attenuate or amplify these partial tones according to the wishes of the sound designer (“subtractive synthesis”). In the context of physical modeling, the oscillator assumes, e.g., the role of a vibrating string of a piano. The sound body corresponding thereto is then emulated, for example by means of a filter, whereas, in the context of additive synthesis, the oscillator is a sine wave of aspecific frequency, amplitude and phase. The additive synthesis generates complex waveforms through addition of many of such simple oscillators. Further ways of proceeding and a mixture thereof for sound generation are typically used in the context of a synthesizer.
The common methods of synthetic sound generation are based on the use of algorithms controlled by parameters fixed by the user. These algorithms generate the waveform on which the output is based, its changing over time as well as over the frequency and the latter's changing over time. The nature of the resulting waveform is usually not visible and not reconstructable to the user, or at best to a limited degree only, from the oscillator base form. The conventional methods can, therefore, be considered as “blackbox” methods. In this sense, the blackbox provides to the user only some parameters by means of which the user can define or modify the resulting tone, within the framework of the possibilities of the parameters provided. The user has no insight into, or influence upon, the internal procedures in the generating process of the tone. The user can just make the result visible by an oscilloscope or by sampling.